We have been studying the mechanism of DNA synthesis by virion associated reverse transcriptase with whole virions and in avian sarcoma virus-infected quail tumor cells. Our results indicate that in both infected cells and virions, poly-A is removed only when DNA synthesis is allowed and plus strand synthesis probably begins after poly-A removal. We have also generated restriction enzyme maps of unintegrated viral supercoiled DNA. These maps are useful in integration studies. Studies on viral gene expression indicate that in the presence of src gene product dibutyryl cyclic AMP supresses intracellular levels of avian sarcoma virus-specific RNAs, which probably explains why Bt2cAMP reverses transformed cells to normal phenotype. Our recently initiated experiments with 5-methylcytidine indicate that a proper balance between the concentrations of viral RNA and viral proteins is to be maintained in order to get high virus yields. Even a slight perturbation of this ratio diminishes the amounts of virus that are released into the medium.